Marijuana May Harm Intelligence in Teen Users, New Study Finds

A long-term study out of New Zealand has found that teens using marijuana on a regular basis may suffer from lowered intelligence as adults. Researchers followed 1,037 individuals, born between 1972 and 1973, for nearly four decades, analyzing them for the effects of persistent marijuana use on neuropsychological functioning. The participants, approximately five percent of which began using marijuana as teenagers, were given IQ tests at age 14, before any had begun using the drug, and again at 38, and were additionally surveyed at ages 18, 21, 26, and 38 about their drug use.

The study found that those who had smoked pot at least four times a week throughout the study suffered, on average, a loss of eight IQ points as adults. Researchers said that the intelligence loss did not appear to be associated with other factors such as the use of other drugs or alcohol, or the educational achievement of the participants.

The study also found a loss of intelligence quotient among participants who had stopped their use of marijuana sometime during the study. When researchers tested these participants at the age of 38, they found that their IQs were lower than at the beginning of the study, indicating that a cessation of pot smoking did not reverse the damage done earlier by the drug. By contrast, participants who began smoking marijuana as adults suffered either a minimal or no drop in intelligence or functioning.

“Researchers hypothesize that cannabis affects the hippocampus and prefrontal cortex, where learning, memory, and planning occur,” reported ModernMedicine.com, “and that teenagers are more susceptible to marijuana’s effects on the brain than older adults. They say their study highlights the importance of refraining from cannabis use during adolescence and the need for policies that encourage teenagers to stop using the drug altogether.”

Madeline H. Meier, a psychologist at Duke University in North Carolina and the study's lead author, noted that the “effect of persistent cannabis use on intellectual functioning is really confined to adolescents, [which] suggests that adolescents, in particular, are vulnerable to the effect of cannabis.”

Meier said that the results of her study seem to indicate that marijuana use “is not harmless, particularly for adolescents.” She said that while an eight point decrease in IQ may seem somewhat negligible when 100 is the average, such a drop would put an individual in 29th percentile rather than the 50th — a significant decrease. Since a higher IQ correlates to better education, career, income, and health, “somebody who loses eight IQ points as an adolescent may be disadvantaged ... for years to come,” Meier said.

ABC News reported that while the study concentrated on young people from New Zealand, “the findings could be extended to adolescents in the United States as well. According to statistics released in June by the U.S. Centers for Disease Control and Prevention, American teenagers today are more likely to be using marijuana than tobacco products. Of particular worry is the attitude that marijuana is one of the more harmless drugs.”

Baptist Press News, an online news organ of the Southern Baptist Convention (SBC), reported that the study's findings come as several states have upcoming ballot initiatives to legalize marijuana. “Voters in Colorado, Washington and Oregon will determine Nov. 6 if they want to legalize marijuana for recreational use,” the news site reported. “Arkansas and Massachusetts voters, meanwhile, will decide whether to legalize marijuana for medical use. Medical marijuana already is legal in 17 states and the District of Columbia.”

Baptist Press News noted that, according to the U.S. Substance Abuse and Mental Health Service Administration, more than half of marijuana users in the U.S. are teens, with a number of studies showing such statistics as:

• Some 2.6 million Americans 12 and older use marijuana, with 58 percent of them under the age of 18.

• Forty percent of American teens have smoked pot in the last year, an alarming increase from 31 percent in 2008.

• Persistent marijuana use by teens has increased by 47 percent in the past four years, to around 27 percent of the teenage population.

• Nearly three-quarters of all U.S. teens say they have friends who are regular marijuana users.

Meier said that the findings of her study demonstrate that “increasing efforts should be directed toward delaying the onset of cannabis use by young people, particularly given the recent trend of younger ages of cannabis-use initiation in the United States and evidence that fewer adolescents believe that cannabis use is associated with serious health risk.”

Barrett Duke, vice president of public policy and research with the SBC's Ethics and Religious Liberty Commission, told BP News that the efforts to legalize marijuana is sending the wrong message to young people. “Legalization of marijuana will assure its greater availability,” he said. “Too many teens are already limiting their futures by using marijuana. We shouldn't do anything to add to their numbers. Rather we should do all we can to prevent the tragic results of marijuana use.”

Constitutionally speaking, states do have the authority to make marijuana, along with substances such as tobacco and alcohol, legal or illegal. And since marijuana use among teens is on the rise despite it being illegal, a more effective approach to protecting teens from this apparently destructive vice would likely be through the influence of education, families, churches, and other groups.

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